Light sensitive diazotype compositions containing alumina pigments



United States Patent Patented Sept. 24, 1957 LIGHT SENSITIVE DIAZQTYPE CGMPOSITION S CONTAINING ALUMINA PIGMENTS Joseph Edward Frederick, Johnson City, N. Y., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application December 22, 1953, Serial No. 399,815

6 Claims. (Cl. 96-49) The present invention relates to light sensitive diazotype materials, and especially to the use of finely divided alumina dispersed in the sensitizing solutions for said materials in order to enhance the density of the azo dye images produced in such materials.

The manufacture of the usual light sensitive diazotype materials involves the application to a fibrous base, such as paper, of a sensitizing solution containing as its main ingredients alight sensitive diazonium compound and an azo dye coupling component. In the processing of such materials they are exposed to light under a pattern to decompose the light sensitive diazonium compound where the light is transmitted by the pattern. Subsequently, a positive dye image is formed by coupling residual diazonium compound and azo coupler in an alkaline medium, preferably ammonia gas.

The ease and cheapness in the manufacture and processing of such materials speak for themselves, and have led to the growth of a substantial industry in the same. Yet, from its very inception this industry has been plagued by one facet of the manufacturing operation to which considerable effort has been contributed in order to find a solution.

It is manifest that the process, being What it is, dye image density, is a direct function of the concentration of diazo in the image areas. It is equally manifest that the extent of destruction and, therefore, the printing speed will depend upon the availability of the diazonium salts to the transmitted light, i. e., the degree to which the diazonium salts accumulate and are retained at or near the surface of the base.

The very nature of the process of manufacturing the diazotype materials, however, is incompatible with such accumulation and retention of the diazonium salts at the base surface. Thus, the bases are generally fibrous in nature and the sensitizing components are applied thereto from an aqueous solution. Consequently, the components of the solutions strike into the base, thereby re ducing their availability to the exposure light. In addition, by so striking through, they produce an image; of low density and a sensitized material with a low printing speed.

This problem has been recognized for many years, and, in this connection, reference is made to British Patent 318,511, dated August 7, 1930, which, in referring to preparation of light sensitive diazotype material, states:

Even when working very quickly, by for instance scraping away at once the excess of sensitizing solution, and quickly drying, the said solution penetrates to a fairly considerable depth into the thickness of the paper.

The British patentee suggested as a possible solution the coating of the base with a layer of gelatin and the appli cation to the gelatin layer ofthe sensitizing components dissolved in low boiling solvents. It was his theory that the solvents would evaporate so quickly that the sensitizer would be retained on the surface of the gelatin. This proposal, involving as it does extra coating steps and the use of expensive solvents, never received recognition by the industry.

In U. S. P. 2,709,655 dated May 31, 1955 entitled Diazotype Photoprinting Material, it is proposed that image density in diazotype materials be augmented by the application of a precoat of finely divided alumina pigment having a particle size up to 10 microns with a film-forming lyophilic basic-to-amphoteric nitrogenous binder, drying the precoat and applying the sensitizing solution thereto. In operating in this fashion it was found that adequate results were only obtained by the maintenance of a particular ratio of alumina pigment to hinder, to wit, 1 to 3 parts of the pigment per part of the binder. Among the binders which I disclosed in the stated relationship are sodium caseinate, gelatin, glue, and Water soluble condensation products of formaldehyde with organic bases such as dicyandiamide, guanidine, melamine and the like.

The binders, the use of which is contemplated in my copending application, are incompatible with the sensitizing solution. It is for this reason that the pigment and binder are applied as a precoat to the base. Such operation injects an additional and unwanted coating step and also gives rise to difficulties in maintaining the coating machines free from binder. The manufacturing procedure is also complicated by reason of the fact that an item is incorporated (binder) having no direct bearing on the processing of light sensitive materials. Consequently, while my prior disclosure covers a method which does enhance dye density, the solution is far from optimum for the indicated reasons. 7

It has been previously proposed by von Glahn and Stanley in their U. S. P. 2,566,709 to improve dye density by employment in the sensitizing composition, per se, of colloidal silica, colloidally dispersed in such composition. This process eliminated the extra coating step of my prior application but failed to provide, by use of the silica employed, the results desired for a number of reasons. Thus, the aqueous dispersion of the colloidal silica added to the sensitizing composition tenaciously retains the water in the pores thereof. As a result less than optimum quantities of the sensitizer are absorbed by the silica grains due to the inability of the sensitizer to displace the Water. Finally, the colloidal silica forms a continuous film -of discrete particles on the base, giving rise to curl and brittleness. The disadvantages inherent in the von Glahn and Stanley procedure would, therefore, lead to the inevitable conclusion that a commercially satisfactory method for improving dye density could not be effected through use of a very finely divided pigment in the coating solution.

It has now been discovered, and most unexpectedly so, that this conclusion is inapplicable where the finely divided pigment is alumina, and that it is possible to greatly improve image density without resort to binders or other contaminates, and without encountering the disadvantages of the procedures of Von Glahn and Stanley and that disclosed in my prior application, by dispersing in the aqueous sensitizing solution an almost chemically pure alumina composed of extremely fine-sized, well-defined particles and then coating the resulting dispersion onto a suitable base.

The manufacture of diazotype materials in this fashion, said-diazotype materials, and the processing thereof, constitute the purposes and objects of the present invention.

The alumina, the use of which is contemplated herein, is any finely divided alumina having a particle size ranging from 5 microns down to and including alumina in the entire colloidal range. The alumina may be in any of its various crystalline forms or mixtures thereof. Preferably,

3 the alumina is chemically pure, consisting of about 99% or more of aluminum oxide.

One form of alumina which I have found to be exceedingly effective is that sold by Godfrey L. Cabot Company of Boston, Massachusetts, under the trademark Alon. This productis essentially A1203 99% pure, being a mixture of various crystalline forms of alumina. The material has a particle ,size ranging from .02 to .04 micron and a surface area of 30-70 square meters per gram. It is to be,understood, however, that this is merely an illustration of a readily available material for my purpose, and that any other alumina having the stated particle size and being substantially chemically pure will serve as well.

The alumina may be added to the sensitizing composition in the form of a dry powder and then dispersed by high speed agitation or the like until the resulting composition is homogeneous. Conversely, the alumina may be separately dispersed by slurrying with water or a small portionof the sensitizing solution to produce therein a uniformly homogeneous paste which is added to the slurry of the sensitizing composition with stirring.

The quantity of the alumina which is added may range from about 1-10% by weightof the sensitizing composition. Best results, however, are obtained when the alumina is present in a concentration of from about 2.5 to 5.5% by weight of thesensitizing solution.

The sensitizing solution is applied to the base by any convenient means, as, for instance, roller application, spraying, brush coating or the like. Care must be taken to ensure that the excess is doctored ofl. either with an air knife, doctor blade or similar means.

In the preparation of the sensitizing solutions I may use any of the customary light sensitive diazonium compounds, and, in this connection, reference is made to the compounds disclosed in U. ,S. P. 2,501,874 and in the article by Van der Grinten, Photographic Journal, vol. 9213, 1952, page 46. Examples of suitable diazo compounds are those derived from p-amino diphenylamine', p-phenylene-diamine sulfonic acid, lp-(N-hydroxyethyl-N- methylamiuo) aniline, p-(N hydroxyethyl-N-ethylamino) aniline, p-amino-N-ethyl-otoluidine, p-diethylaminoaniline, p-(N-benzyl-N-ethyl) aniline and the like. It is evident that these diazos are of the class of p-phenylenediamines, in which one nitrogen atom is monoor disubstituted. According to customary procedure the diazo compounds are employed in the form of their stabilized salts, such as the zinc chloride double salt, cadmium salt, the chlorobenzene sulfonate, the tin chloride double salt, the borofiuoride salt and the like.

The particular coupling components utilized in the sensitizing compositions are not critical to the invention. Thus, usual coupling components are satisfactory for my purpose. Examples of suitable couplers are resorcinol, resorcinol sulfonic acid, di-sodium salt of 2-naphthol-3,6- disulfonic acid, phloroglucinol, 2,3-dihydroxynaphthalenefi sulfonic acid and the like.

The coating solution may also contain the various adjuncts usual in the manufacture of light senistive diazotype materials. These include metal salts for intensification of the dyestutf image, such as ammonium sulfate, nickel sulfate, zinc chloride and the like; stabilizing agents such as thiourea, thiosinamine; naphthalene trisulfonic acid and the like; acids acting to retard precoupling such as acetic acid, boric acid, tartaric acid and the like; hygroscopic agents such as glycol, glycerin and the like; and wetting. agents such as ,saponin, lauryl sulfonate, keryl benzene sulfonate, the oleic acid amide of N-methyl taurine and the like.

The base to which the coating solution is applied may be any of those which have been previously suggested for employment in the diazo type field. Examples of such bases are high-grade, all-sulfite paper, rag paper, rayon The use of the finely divided alumina in the sensitizing composition leads to manifold advantages, none of which could be deduciblc from prior work, particularly my prior application described above and the work of von Glahn and Stanley. Thus, the alumina may be added directly to the diazotype sensitizing solution and the base sensitized in a one-step operation. This eliminates the precoating operation whereby a considerable saving in cost and production time is effected. At the same time, there is no sacrifice in quality of the product when compared to the precoated product of my prior case.

The alumina pigment, when it is properly dispersed in the sensitizing composition, remains suspended without the necessity of agitation or circulating systems which are a necessary adjunct for pigments of larger particle size.

The alumina when dispersed in the diazotype solutions adsorbs the component parts of the solution onto and into the pores thereof. When the sensitizing solution, containing the alumina, is properly applied to the base a greatly improved physical and chemical distribution of the dye components results. This, in turn, means the attainment of markedly improved density with no sacrifice in printing speed or a much more rapid printing speed with maintenance of the original density level.

The inert alumina, when incorporated into the sensitizing compositions, has the ability to inhibit the penetration of the sensitizer into porous base materials. In other words, the alumina acts to retain the sensitizing components in the inner particles of the alumina and at the surface of the base material whereby most effective results ensue.

The prints produced by exposing and developing the coated paper have greatly improved dye density over prints produced with the same sensitizing solutions but free from alumina. My prints, moreover, are free from crocking, eliminating the necessity for a binder, it being noted that a binder is largely responsible for sticky prints which do not process satisfactorily through most reproduction machines. My prints possess a white background resulting in improved contact. They also have a desirable matte appearance free from feathering to ink line and possess excellent pencil tooth.

The diazotype materials containing alumina applied as stated have developing characteristics superior to those free from alumina.

One of the most outstanding advantages of sensitizing compositions containing the alumina contemplated herein is the possibility of extending diazotype coatings to very desirable bases which heretofore could not be so employed. The inability of the art to use such bases was attributable to a tendency of the bases to repel the coating compositions, for one reason or another, such as supercalendering of the surface, impregnation of. the base with hydrophobic materials and the like. In anycase, the coating of such papers in the past led to little success and in many instances the coating compositions were shed by the surfaces involved to an extent equivalent to the shedding of water by the proverbial ducks back. Bases of the type which I have in mind are, for example, of highly calendered rag paper, particularly when transparentized by use of resinous materials, waterproof tracing paper, tracing clothcalendered with hydrophobic lubricants and the like. Despite the factthat there has been a heavy demand for diazotype materials in which such materials operate as a base, due to the inability of the art to uniformly coat such bases without obtaining a mottled effect, they have been rarely used.

It has now been found, however, that the coating compositions containing the alumina previously mentioned eliminate the tendency of the bases to repel the coating compositions and to do away with the nonuniform coatings previously obtained. The particular reason why the alumina operates as it does with the specified surfaces is not known and has not been completely investigated. Conceivably, the phenomenon mentioned is bottomed on a surface abrasion by the alumina particles which render the surface sufliciently matte in finish so that a smooth coating may be obtained. In any event, regardless of the theory, the fact is that by employing the alumina it is possible to use papers of hydrophobic nature which heretofore had been considered of no utility in this field because of their resistance to uniform coatings. Manifestly, this extension of the diazotype coating technique to extremely desirable bases is a matter of great magnitude from the standpoint of the customer and manufacturer.

The following examples will serve to illustrate the invention, but it is to be understood that the invention is not restricted thereto.

Example 1 A sensitizing solution for blue-line prints was prepared from the following components:

Water cc 100 Ethylene glycol cc 5 Citric acid grams 5 Thiourea do 5 Zinc chloride I do..." 5 2,3-Dihydroxynaphthalene-6-sulfonic acid. do 4 p-Diazo dimethyl aniline u do 2 Saponin do 0.1

Example II High-grade, all-sulfite bond paper is coated with a sepia line sensitizing solution of the following composition:

Water PP 100 Ethylene glycol cc 5 Citric acid grams" 7 Boric acid do 2 Thiourea do 5 Zinc chloride dn 5 Resorcinol do 2 6 p-Diazo-(N-hydroxyethyl N ethylamino) aniline grams 4.5 Saponin do 0.1 Fine sized alumina do 3.5

The alumina is dispersed in the sensitizing solution as in Example I.

The sepia line prints obtained from the coatings of this Example have characteristics similar to those of Example 1.

Various modifications of the invention will occur to persons skilled in the art. Thus, as is evident, the alumina may be used with other formulations than those designated in the Examples, i. e., black and red-line formulations. 1, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

I claim:

1. Sensitizing compositions for light sensitive diazotype materials comprising an aqueous dispersion of a light sensitive diazonium compound, an azo dye coupling component and a substantially chemically pure aluminum oxide having a particle size ranging from 5 microns downward.

2. The composition as defined in claim 1, wherein the aluminum oxide is present in an amount ranging from about 1 to 10% by weight of the sensitizing solution.

3. The composition as defined in claim 1, wherein the aluminum oxide is present in an amount ranging from about 2.5 to 5.5% by weight of the sensitizing solution.

4. Light sensitive diazotype materials comprising a base coated with the sensitizing composition of claim 1.

5. Light sensitive diazotype materials comprising a base coated with the sensitizing composition of claim 2.

6. The process of producing azo dye images having a matte appearance and high density and brightness which comprises exposing under a pattern a base coated with a sensitizing composition comprising an aqueous dispersion of light sensitive diazonium compound, an azo dye coupling component and a substantially chemically pure aluminum oxide having a particle size ranging from 5 microns downward, and subjecting the exposed base to an alkali to effect azo dye formation between the coupling component and residual diazonium compound.

References Cited inthe file of this patent UNITED STATES PATENTS 2,205,991 Neugebauer et al. June 25, 1940 2,552,354 Von Glahn et a1 May 8, 1951 2,665,985 Sus Jan. 12, 1954 2,672,418 Neugebauer et a1 Mar. 16, 1955 

6. THE PROCESS OF PRODUCING AZO DYE IMAGES HAVING A MATTE APPEARANCE AND HIGH DENSITY AND BRIGHTNESS WHICH COMPRISES EXPOSING UNDER A PATTERN A BASE COATED WITH A SENSITIZING COMPOSITION COMPRISING AN AQUEOUS DISPERSION OF TIGHT SENSITIVE DIAZONIUM COMPOUND, AN AZO DYE COUPLING COMPONENT AND A SUBSTANTIALLY CHEMICALLY PURE ALUMINUM OXIDE HAVING A PARTICLE SIZE RANGING FROM 5 MICRONS DOWNWARD, AND SUBJECTING THE EXPOSED BASE TO AN ALKALI TO EFFECT AZO DYE FORMATION BETWEEN THE COUPLING COMPONENT AND RESIDUAL DIAZONIUM COMPOUND. 